The above referenced applications and patents describe embodiments of interrelated systems designed to deliver high definition television (HDTV) source signals utilizing conventional signal media. In other words, they provide solutions to the problem of taking a wide bandwidth HDTV source signal, converting it to a signal with a more narrow bandwidth, for example a 9.5 MHz satellite channel or a 6 MHz. terrestrial broadcasting channel (or portion thereof), in order to transmit/receive or record/reproduce it, and then recreating an HDTV display.
Parent application No. 239,148 described an embodiment of a so called "augmentation" or two channel approach to the transmission (or recording) and reception (or reproduction) of HDTV. This type of approach is most widely discussed as a method for terrestrial broadcasting HDTV in a manner which maintains compatibility with conventional (for example NTSC) television receivers.
HDTV source signals provide a wider aspect ratio picture (for example 16:9) and higher horizontal resolution (for example 495 TVL corresponding to about 16.8 MHz.) than do conventional television signals which have an aspect ratio of 4.3. The HDTV source signal can be a sequentially scanned (1:1) or interlaced (2:1) signal of, for example 525 or 1050 lines respectively, at a field rate which is compatible with conventional standards, for example 59.94 fields per second for NTSC. A conventional television signal (for example NTSC) provides a 525 line interlaced signal at that field rate.
The parent application describes a system in which an HDTV source signal is processed by an encoder to form two separate signals. The encoder derives from the wide aspect ratio source picture, a plurality of main signal components derived from selected lines of the HDTV source picture (i.e. Y1 and Y3) of every four lines of each field. These components, which include corresponding chrominance components are combined to create a composite (e.g. NTSC) signal. These main signal components are related to the center portion of the source picture having an aspect ratio of 4:3, and at least one, but normally two, panel portions comprising the balance of the wide aspect ratio source picture. The encoder also derives a plurality of line differential (LD) components from the source picture which are similarly divided into center and panel components. A high frequency luminance signal (Yh) is derived from one out of every four source lines. Digital audio and synchronization signals (DSS) are also provided by the encoder.
As described in the parent application, the main center components and the LD center components are modulated in quadrature with a first picture carrier in order to form a center signal which is receivable on conventional (i.e. NTSC) receivers. This center signal is a vestigial sideband (VSB) signal. The main panel portions (PL1/PR1 and PL3/PR3) of the source signal lines 1 and 3 respectively are quadrature modulated with a subcarrier to form a main panel double sideband signal (DSB). The LD panel portions (LDL2/LDR2 and LDL4/LDR4) for lines 2 and 4 respectively, are quadrature modulated with a subcarrier to form an LD panel DSB signal, double sideband being necessary due to the quadrature modulation.
In processing the augmentation signal therefore, the main panel components are processed separately from LD panel components, unlike the center signal processing where main and LD components are combined The Yh component is heterodyned onto a subcarrier and time multiplexed with the main panel and LD panel DSB signals to form a time multiplexed augmentation component which is then frequency multiplexed with another subcarrier which has been modulated by the DSS component, thereby forming an augmentation signal which, when combined with the center signal in an HDTV decoder, will provide an HDTV display.
A problem which is inherent in the packaging taught by the parent application however, is that augmentation information related to panel portions of the HDTV source signal is processed differently from the information related to the center portion. The main panel information and the LD panel information are processed separately as separate DSB signal components. On the other hand, the main center and the LD center components are quadrature modulated together to form the VSB center signal. It has been found that processing the center and panel HDTV portions in this dissimilar fashion, can increase the potential for artifacts in the reconstructed HDTV display which might arise from a differences in the transmission paths of the center and augmentation signals.
It is therefore an object of the instant invention to provide an HDTV augmentation system which is more robust and less susceptible to artifacts by packaging the main and augmentation signals in an improved fashion.